1. Field of the Invention
This invention relates to improvements in a continuously variable transmission apparatus incorporating therein, for example, a toroidal type continuously variable transmission utilized as a transmission for an automobile, and realizes compact structure capable of securing the durability of the constituent members of the toroidal type continuously variable transmission.
2. Related Background Art
For example, it has been studied to use a toroidal type continuously variable transmission as schematically shown in FIGS. 6 and 7 of the accompanying drawings as a transmission for an automobile. This toroidal type continuously variable transmission, as disclosed, for example, in Japanese Laid-Open Utility Model Application No. 62-71465, has an input disc 2 supported concentrically with an input shaft 1, and has an output disc 4 fixed to the end portion of an output shaft 3 disposed concentrically with the input shaft 1. Inside a casing containing the toroidal type continuously variable transmission, there are provided trunnions 6, 6 pivotatally moved about pivots 5, 5 on axes transverse to the input shaft 1 and the output shaft 3.
That is, the pivots 5, 5 of each trunnion are provided coaxially with each other on the outer sides of the opposite end portions of the trunnion. Also, the base end portions of displaceable shafts 7, 7 are supported on the central portions of the trunnions 6, 6, and the trunnions 6, 6 are pivotally moved about the pivots 5, 5, whereby the angles of inclination of the displaceable shafts 7, 7 are made adjustable. Power rollers 8, 8 are rotatably supported around the displaceable shafts 7, 7 supported on the trunnions 6, 6. These power rollers 8, 8 are sandwiched between the input and,output discs 2 and 4. The inner sides 2a and 4a of these input and output discs 2 and 4 which are opposed to each other have their cross-sections forming concave surfaces obtained with arcs centering about the pivots 5 rotated about the center axes of the discs. The peripheral surfaces 8a, 8a of the power rollers 8, 8 which are formed into spherical convex surfaces, are made to bear against the above-mentioned inner sides 2a and 4a, respectively.
A loading cam type pressing device 9 is provided between the input shaft 1 and the input disc 2, and by this pressing device 9, the input disc 2 can be resiliently pressed toward the output disc 4. This pressing device 9 is comprised of a cam plate 10 rotated with the input shaft 1, and a plurality of (e.g. four) rollers 12 held by a holder 11. A cam surface 13 which is an uneven surface extending in the circumferential direction is formed on one side (the left side as viewed in FIGS. 6 and 7) of the cam plate 10, and a similar cam surface 14 is also formed on the outer side (the right side as viewed in FIGS. 6 and 7) of the input disc 2. The plurality of rollers 12, 12 are supported for rotation about radial shafts relative to the center of the input shaft 1.
When during the use of the toroidal type continuously variable transmission constructed as described above, the cam plate 10 rotates with the rotation of the input shaft 1, the plurality of rollers 12 are pressed against the cam surface 14 formed on the outer side of the input disc 2 by the cam surface 13. As a result, the input disc 2 is pressed against the plurality of power rollers 8, 8 and at the same time, on the basis of the pair of cam surfaces 13, 14 and the plurality of rollers 12, 12 being urged against each other, the input disc 2 is rotated. The rotation of this input disc 2 is transmitted to the output disc 4 through the plurality of power rollers 8, 8, whereby the output shaft 3 fixed to this output disc 4 is rotated.
When the rotational speed ratio (transmission gear ratio) between the input gear 1 and the output gear 3 is to be changed and deceleration is to be effected between the input shaft 1 and the output shaft 3, the trunnions 6, 6 are pivotally moved about the pivots 5, 5 and the displaceable shafts 7, 7 are inclined so that the peripheral surfaces 8a, 8a of the power rollers 8, 8 may bear against that portion of the inner side 2a of the input disc 2 which is toward the center thereof and that portion of the inner side 4a of the output disc 4 which is toward the outer periphery thereof, as shown in FIG. 6. When conversely, acceleration is to be effected, the trunnions 6, 6 are pivotally moved and the displaceable shafts 7, 7 are inclined so that the peripheral surfaces 8a, 8a of the power rollers 8, 8 may bear against that portion of the inner side 2a of the input disc 2 which is toward the outer periphery thereof and that portion of the inner side 4a of the output disc 4 which is toward the center thereof, as shown in FIG. 7. Also, if the angle of inclination of the displaceable shafts 7, 7 is made medium between FIGS. 6 and 7, a medium transmission gear ratio will be obtained between the input shaft 1 and the output shaft 3.
FIGS. 8 and 9 of the accompanying drawings show a more specific example of the toroidal type continuously variable transmission described in the microfilm of Japanese Utility Model Application No. 63-69293 (Japanese Laid-Open Utility Model Application No. 1-173552). An input disc 2 and an output disc 4 are rotatably supported around a tubular input shaft 15 through needle bearings 16 and 16, respectively. Also, a cam plate 10 is spline-engaged with the outer peripheral surface of an end portion (the left end portion as viewed in FIG. 8) of the input shaft 15 and blocks the movement away from the input disc 2 by a flange portion 17. This cam plate 10 and rollers 12, 12 together constitute a pressing device 9 for rotating the input disc 2 on the basis of the rotation of the input shaft 15 while pressing it toward the output disc 4. An output gear 18 is coupled to the output disc 4 by keys 19, 19 so that the output disc 4 and the output gear 18 may be rotated in synchronism with each other.
The opposite end portions of a pair of trunnions 6, 6 are supported on a pair of support plates 20, 20 for pivotal movement and displacement in the axial direction thereof (the front to back direction as viewed in FIG. 8, and the left to right direction as viewed in FIG. 9). Displaceable shafts 7, 7 are supported in circular holes 21, 21 formed in the intermediate portions of the trunnions 6, 6. These displaceable shafts 7, 7 have support shaft portions 22, 22 and pivotal support shaft portions 23, 23 parallel to each other and eccentric with respect to each other. The support shaft portions 22, 22 are rotatably supported inside the circular holes 21, 21 through radial needle bearings 24, 24. Also, power rollers 8, 8 are rotatably supported around the pivotal support shaft portions 23, 23 through discrete radial needle bearings 25, 25.
The pair of displaceable shafts 7, 7 are provided at positions opposite by 180.degree. with respect to the input shaft 15. Also, the directions in which the pivotal support shaft portions 23, 23 of these displaceable shafts 7, 7 are eccentric with respect to the support shaft portions 22, 22 are the same direction (left and right converse directions as viewed in FIG. 9) with respect to the direction of rotation of the input and output discs 2 and 4. Also, the direction of eccentricity is a direction substantially orthogonal to the direction of disposition of the input shaft 15. Accordingly, the power rollers 8, 8 are supported for some displacement in the direction of disposition of the input shaft 15. As the result, even when the power rollers 8, 8 tend to be displaced in the axial direction of the input shaft 15 (the left to right direction as viewed in FIG. 8, and the front to back direction as viewed in FIG. 9) due to the resilient deformation of each constituent member based on a great load applied to each constituent member in a state in which the rotational force is being transmitted, this displacement can be absorbed without any unreasonable force being applied to each constituent member.
Also, between the outer sides of the power rollers 8, 8 and the inner sides of the intermediate portions of the trunnions 6, 6, thrust ball bearings 26, 26 and thrust needle bearings 27, 27 are provided in succession from the outer sides of the power rollers 8, 8. The thrust ball bearings 26, 26 permit the rotation of the power rollers 8, 8 while supporting the load in the thrust direction applied to the power rollers 8, 8. The thrust needle bearings 27, 27 permit the pivotal support shaft portions 23, 23 and outer races 28, 28 constituting the thrust ball bearings 26, 26 to be pivotally moved about the support shaft portions 22, 22 while supporting thrust loads applied from the power roller 8, 8 to the outer races 28, 28.
Further, driving rods 29, 29 are coupled to one end portion (the left end portion as viewed in FIG. 9) of the trunnions 6, 6, and driving pistons 30, 30 are secured to the outer peripheral surfaces of the intermediate portions of these driving rods 29, 29. These driving pistons 30, 30 are oil-tightly fitted in driving cylinders 31, 31.
During the operation of the toroidal type continuously variable transmission constructed as described above, the rotation of the input shaft 15 is transmitted to the input disc 2 through the pressing device 9. The rotation of this input disc 2 is transmitted to the output disc 4 through the pair of power rollers 8, 8 and further, the rotation of this output disc 4 is taken out from the output gear 18. When the rotational speed ratio between the input shaft 15 and the output gear 18 is to be changed, the pair of driving pistons 30, 30 are displaced in opposite directions. With the displacement of these driving pistons 30, 30, the pair of trunnions 6, 6 are displaced in opposite directions, and for example, the lower power roller 8 as viewed in FIG. 9 is displaced to the right side as viewed in FIG. 9 and the upper power roller 8 as viewed in FIG. 9 is displaced to the left side as viewed in FIG. 9. As the result, the direction of the force in the tangential direction acting on the portions of contact between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner sides 2a and 4a of the input disc 2 and the output disc 4 changes. With this change in the direction of this force, the trunnions 6, 6 are pivotally moved in opposite directions about the pivots 5, 5 pivotally supported by the support plates 20, 20. As the result, as shown in FIGS. 6 and 7, the position of contact between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner sides 2a and 4a changes and the rotational speed ratio between the input shaft 15 and the output gear 18 changes.
When the transmission of the rotational force is effected between the input shaft 15 and the output gear 18 as described above, the power rollers 8, 8 are displaced axially of the input shaft 15 on the basis of the resilient deformation of each constituent member, and the displaceable shafts 7, 7 pivotally supporting these power rollers 8, 8 slightly rotated about the support shaft portions 22, 22. As a result of this rotation, the outer sides of the outer races 28, 28 of the thrust ball bearings 26, 26 and the inner sides of the trunnions 6, 6 are displaced relative to each other. The force required for this relative displacement is small because the thrust needle bearings 27, 27 are present between these outer and inner sides. Accordingly, the force for changing the angle of inclination of the displaceable shafts 7, 7 as described above may be small.
When the toroidal type continuously variable transmission constructed and acting as described above is to be incorporated into for an automobile, it has heretofore been proposed as described in Japanese Laid-Open Patent Application No. 1-169169 and Japanese Laid-Open Patent Application No. 1-282266 to construct the continuously variable transmission apparatus in combination with a planetary gear mechanism. FIG. 10 of the accompanying drawings schematically shows the basic construction of such a heretofore proposed continuously variable transmission apparatus. The driving shaft 33 (crank shaft) of an engine 32 which is a drive source is coupled to the input shaft 15 (see FIGS. 8 and 9) of a toroidal type continuously variable transmission 34 having the construction as shown in FIGS. 8 and 9. Also, an output shaft 36 for driving the driving wheels through a differential gear 35 (see FIG. 1 of the accompanying drawings which shows an embodiment of the present invention) is coupled and fixed to a sun gear 38 (see FIG. 1) of a planetary gear mechanism 37 and is rotated with this sun gear 38.
Also, the output disc 4 (see FIGS. 1, 6, 7 and 8) of the toroidal type continuously variable transmission 34 and a carrier 39 (see FIGS. 1 and 2) of the planetary gear mechanism 37 are connected together so as to be capable of transmitting the rotational force by a first power transmitting mechanism 41. Also, the driving shaft 33 and the input shaft 15 and a ring gear 42 (see FIGS. 1 and 2) of the planetary gear mechanism 37 can be connected together so as to be capable of transmitting the rotational force by a second power transmitting mechanism 43. Provision is further made of changeover means capable of changing over the speed change state of the driving shaft 33 and the input shaft 15 and the output shaft 36 among three modes, i.e., the high-speed running mode, the low-speed running mode and the receding mode. The ratio .beta./.alpha. between the reduction ratio .alpha. of the first power transmitting mechanism 41 and the reduction ratio .beta. of the second power transmitting mechanism 43 is made substantially equal to the reduction ratio during the maximum acceleration of the toroidal type continuously variable transmission 34 (the reduction ratio between the input shaft 1 and the output shaft 3 in the state shown in FIG. 6) i.sub.H.
The continuously variable transmission apparatus as shown in FIG. 10 is called the power split type and in the low-speed running mode, it transmits all the power among the driving shaft 33 and the input shaft 15 and the output shaft 36 through the toroidal type continuously variable transmission 34. In contrast, in the high-speed running mode, it transmits the power through the planetary gear mechanism 37, and circulates part of this power from the planetary gear mechanism 37 to the toroidal type continuously variable transmission 34. That is, during the low-speed running, the driving force of the engine 32 is transmitted by only the toroidal type continuously variable transmission 34, and during the high-speed running, the driving force is transmitted by the planetary gear mechanism 37 to thereby reduce the torque applied to the toroidal type continuously variable transmission 34 during the high-speed running. By such construction, the durability of each constituent member of the toroidal type continuously variable transmission 34 can be improved and at the same time, the transmission efficiency of the entire continuously variable transmission apparatus can be achieved.
The continuously variable transmission apparatus of the power split type as described above can achieve the mitigation of the torque transmitted through the toroidal type continuously variable transmission during the high-speed running and can achieve an improvement in durability and an improvement in transmission efficiency. However, it is complicated in structure due to the provision of the first and second power transmitting mechanisms, and it is difficult to make it compact and lightweight.
For example, to make the axial dimensions of the first and second power transmitting mechanisms small to shorten the axial dimension of the continuously variable transmission apparatus, it is preferable that these power transmitting mechanisms not be transmitting mechanisms using a belt or a chain, but gear transmitting mechanisms. On the other hand, when the gear transmitting mechanisms are adopted, it is necessary to effect the transmission of a rotational force between a driving side rotational shaft and a driven side rotational shaft spaced apart from each other without making the gear large in diameter, and to install an idle gear between a driving side gear and a driven side gear to regulate the direction of rotation to a desired direction. With the installation of such an idle gear, an idle shaft for supporting this idle gear becomes necessary, and it becomes difficult to dispose this idle shaft.